This invention generally relates to frequency selectors for a variable frequency tuning system and more specifically is directed to a touch-sensitive selector system for variably controlling the tuning system's rate of change in frequency during the tuning process.
There are several approaches currently available for changing the frequency of the tuning system in a receiver or a transceiver. The traditional and most common method involves a knob or knobs mechanically coupled to one or more variable capacitors included in one or more oscillators which determine the frequency at which the unit receives and/or transmits. The frequency tuned to is displayed by means of a rotary or slide rule dial, or a digital display which is part of a frequency counter.
With the introduction of tuning systems incorporating frequency synthesizers which provide tuning in equal frequency increments, tuning is accomplished by means of a shaft encoder. The shaft encoder is coupled to the rotary selector, providing output pulses in response to the rotation of the selector knob. Frequency display is digital and is available without the use of a frequency counter. The output pulses of the shaft encoder are provided to one or more digital dividers for the incrementing or decrementing thereof, depending on which direction the knob is turned. For good frequency resolution small tuning increments are desirable, while an excessive number of revolutions of the selector knob should not be required in tuning between widely separated frequencies. Although both of these operating characteristics are highly desirable, they are frequently mutually exclusive. However, various approaches have been undertaken in attempting to make these two features compatible in the control selector of a tuning system.
One approach to improving tuning selector performance makes use of a separate knob to select one of the more significant digits, typically the 1 MHz digit, of the desired frequency. This may be accomplished by means of a rotary switch or another shaft encoder. Another approach employs a multi-speed knob with increasing selector knob rotation rates producing larger tuning frequency increments. A disadvantage of this method is that the user is frequently unaware of the rate of change of tuning frequency resulting in decreased tuning accuracy. This shortcoming may be avoided to some extent by the use of a pushbutton which, when pressed, increases tuning frequency increments.
Yet another approach makes use of two pushbutton switches to scan frequencies. One pushbutton is used for scanning up in frequency, while the other is used for scanning down, with frequency increment size either fixed or adjustable. Spinner selector knobs are frequently used in such tuning systems even where pushbutton switches are provided to expedite the tuning process. The spinner knob includes a finger hole near its circumference permitting it to be rapidly rotated when large frequency changes are desired. For fine tuning, the outside of the knob is rotated as desired.
The aforementioned approaches to variable speed tuning have not been the only efforts undertaken to improve the tuning process. The prior art also discloses efforts to facilitate tuning by means of touch control switches. This type of switch is responsive to a user touching a touch plate and changing the capacitance of a touch sensitive capacitive network. A sensing circuit detects the change in capacitance causing the controlled portion of the system to be appropriately regulated. This may, for example, be accomplished by detecting the change in amplitude of an alternating signal coupled through the touch sensitive capacitive network.
One approach to a touch sensitive switch is disclosed in U.S. Pat. No. 4,207,479 to Yamamoto et al. wherein is described a touch sensitive switch particularly adapted for use with Integrated Injection Logic (I.sup.2 L) circuitry. Included therein is a battery power source, a current limiter, an injector and first and second stage transistors supplied with current from the injector. A first touch electrode is coupled to the positive polarity of the battery power source while a second touch electrode is connected to an input terminal of an I.sup.2 L circuit. The first stage switching transistor within the I.sup.2 L circuit structure is normally OFF to minimize power consumption. When human body resistance is interposed between the touch electrodes, a high potential is impressed on the base of the first stage switching transistor which is thereby turned ON. With the injector thus energized current flows into the first stage switching transistor but not into the next stage switching transistor which is turned OFF. In this manner, ON and OFF switching signals are generated. Another approach to a touch control switch arrangement particularly adapted for use in a television receiver is disclosed in U.S. Pat. No. 4,263,618 to Wine. This switch arrangement includes a peak detector having a series connected diode and a shunt connected filter capacitor coupled beween a touch sensitive coupling network and the control portion of a system. An alternating signal is coupled through a capacitive coupling network with an amplitude dependent upon whether or not a user has touched the touch sensitive network. The alternating signal is peak detected by the peak detector to generate a DC control signal for the control portion. While offering various control switch advantages, the aforementioned touch control switch approaches are limited to specific tuning system environments and lack general applicability as a tuning system selector.
The present invention, however, may be used with any conventional tuning system for providing a variable tuning speed capability. It offers the advantages of ease of operation, low cost, and improved user control of receiver/transceiver tuning circuitry.